This invention relates to metallizing paste for use in multi-layered circuit board for mounting integrated circuits (IC), IC-packages, and so forth thereon. More particularly, it is concerned with metallizing paste adaptable to ceramic substrate materials having a thermal expansion coefficient (.alpha.) of 5.0.times.10.sup.-6 /.degree. C. or lower, such as crystallized glass, alumina-glass composite body, SiC, Si.sub.3 N.sub.4, AlN, and so forth.
In recent years, with development in miniaturization, etc. of various electronic apparatuses and appliances, packaging (or mounting) density of those electrical components such as IC, etc. on the circuit board has become higher and higher. Considering, further, mounting of the power semiconductors, etc., quantity of heat generation on the circuit board becomes much greater.
On account of this, the substrate material to be used is also of ceramic having the thermal expansion coefficient (.alpha.) of 5.0.times.10.sup.-6 /.degree. C. or lower (at a temperature ranging from room temperature to 400.degree. C.), examples of which are SiC, Si.sub.3 N.sub.4, AlN, and so forth. In recent years, there has also been developed the substrate made of crystallized glass material.
For such multi-layered substrates and packages of low thermal expansion coefficient, gold-metallization is usually used, onto which metallized layer metal members (such as leads) are joined by use of brazes such as AuSn or AuSi, or solders such as In/Pb and so on.
In the methods of joining the metal members to the substrates utilizing the brazing or soldering (generally referred to as "brazing" hereinafter) materials as mentioned above, there have been problems in its workability and reliability owing to softening of the brazing material by its reheating during joining of IC chips (at the time of die-mounting). It becomes therefore necessary that the metal member be joined by use of a high temperature brazing material (e.g., pure silver brazing). In this case, the paste for the substrate should also be compatible with this brazing material.
However, the gold metallizing pastes which have conventionally been used for the substrates and so on causes an alloy to be formed between the gold and the softened brazing material, when use is made of a high temperature brazing material such as pure silver braze. On account of this, the gold which has been metallized on the surface of ceramic material is dispersed in the brazing material to lower the bonding strength thereof to become unable to maintain it in a preferred amount and to bring about a problem presenting "eroding phenomenon by the brazing material".
Furthermore, as a method for metallizing ceramics, there has been known the so-called "Telefunken Process" utilizing high melting point metals. However, since these metals are, conductors of a high resistance, they are not suitable for metallizing the multi-layered circuit boards, and others.